A statistical investigation of the Anthracomyas of the basal Similis-Pulchra Zone in Scotland

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Abstract
In a recent paper on “the Zonal Distribution of the Non-marine Lamellibranchs in the Coal Measures of Scotland” (Weir and Leitch 1936) the lower boundary of the Similis-Pulchra Zone was defined by a fauna that occurs above the Musselband Coal of the Central Coalfield, above the Three-Foot Coal of Douglas and below the Wee (Hurlford Main) Coal of North Ayrshire. The fauna contains a rich and varied assemblage of Anthracomyas which were determined as A. adamsi Salter sensu lato. In defining the fauna as that of the base of the Similis-Pulchra Zone, reference was made to the fact that in England and Wales the normal A. adamsi is typical of a much higher horizon in the zone (above the Mansfield Marine Band and its equivalents); on the other hand, certain of the associated Carbonicolas ( C. affinis and C. turgida ) are typical of horizons that have been interpreted as high in the Modiolaris Zone (Wright's Affinis Subzone). Referring to the above work, W. B. Wright (1938), from an examination of the illustrations, suggested (a) that the Anthracomya is A. modiolaris and should not have been referred to A. adamsi ; (b) that, considering this and the associated Carbonicolas, the fauna closely approximates to that of the base of his Affinis Subzone, defining therefore the upper boundary of the Modiolaris Zone; and (c) that the reference to A. adamsi was, in any case, unfortunate, as he did not consider it an exactly defined species and that it was “quite within the range of

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